A multilayer blown film for producing labels is known from DE 10 2007 045 117 A1. The layer construction of that film comprises two outer layers of polyethylene and a core layer of a polypropylene blend. The polypropylene blend consists of 5 to 25 wt % of polypropylene homopolyraers (PP-H), 5 to 35 wt % of polypropylene random copolymers (PP-RC), and 40 to 80 wt % of polypropylene block copolymers (PP-BC). A characteristic of the core mixture is the low fraction of polypropylene homopolymers, which promote the flexural stiffness and diecuttability of the material, blended with a large fraction of PP block copolymers, which can be used to manufacture blown films having a high modulus of elasticity and a low haze. The known blown film is flexible and was developed for sharply curved surfaces. Numerous applications require greater flexural stiffness in the label film. In terms of diecuttability as well, the known film is still in need of improvement.
EP 1 919 7 06 B1 discloses a multilayer film for packaging, said film having two outside polyethylene layers and a core layer, The core layer consists of a mixture of polypropylene and a metallocene-catalyzed linear polyethylene (mLLDPE). The propylene is preferably a homopolymer and has a melt flow index of not more than 4 g/10 min (as measured to ISO 1133 at 230° C. with 2.16 kg).
From the art it is known that polypropylene with a melt, flow index higher than 4.0 g/10 min cannot be reliably processed on conventional blown film lines, since stable blown film extrusion is no longer ensured as the melt flow index increases.